Optoelectronic Component

ABSTRACT

An optoelectronic component having a basic housing or frame and at least one semiconductor chip, specifically a radiation-emitting or-receiving semiconductor chip, in a cavity of the basic housing. In order to increase the efficiency of the optoelectronic component, reflectors are provided in the cavity in the region around the semiconductor chip. These reflectors are formed by virtue of the fact that a filling compound filled at least partly into the cavity is provided, the material and the quantity of the filling compound being chosen in such a way that the filling compound, on account of the adhesion force between the filling compound and the basic housing, assumes a form which widens essentially conically from bottom to top in the cavity, and the conical inner areas of the filling compound serve as reflector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/141,721, which was filed on May 31, 2005, which is a continuation ofU.S. patent application Ser. No. 10/611,225 which was filed on Jun. 27,2003 and claims priority to German application No. 102 29 067.9, filedon Jun. 28, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optoelectronic component, inparticular a surface-mountable optoelectronic component, having at leastone semiconductor chip, which emits and/or receives electromagneticradiation, and a reflective compound.

2. Description of the Related Art

Conventionally, in the production of surface-mountable optoelectroniccomponents, by way of example, firstly a prefabricated electricalleadframe is encapsulated by injection-moulding with a suitable plasticsmaterial which forms the basic housing of the component. This basichousing has a cavity (or else chip window) into which leadframeterminals are introduced from two opposite sides. A semiconductor chipthat emits and/or transmits electromagnetic radiation, such as an LEDchip, for example, is bonded and electrically contact-connected on oneof the said leadframe terminals. A transparent or translucent pottingcompound is built into the cavity. This basic form of surface-mountableoptoelectronic components is disclosed for example in the article“SIEMENS SMT-TOPLED für die Oberfláchenmontage” [“SIEMENS SMT-TOPLED forsurface mounting”] by F. Mollmer and G. Waitl, Siemens Components 29(1991), issue 4, pages 147-149.

In the case of such optoelectronic components, it is customary, for thepurpose of increasing the external efficiency, to form the cavity withoblique inner areas which serve as reflector. Depending on the angle ofinclination of the inner areas, the opening of the cavity iscorrespondingly enlarged thereby.

Examples of optoelectronic components with such reflector arrangementsare disclosed for example in the document DE 197 55 734 A1 and thedocument DE 199 18 370 A1.

A similar construction is described in the document DE 195 36 454 A1. Inthis case, a metal chip carrier part on which the semiconductor chip ismounted is provided in a cavity of a basic housing of the component. Awell is formed in the chip carrier part in the region in which thesemiconductor chip is fixed, the inner areas of which well approximatelycorrespond to the form of an inverted truncated cone and form areflector for the radiation emitted by the semiconductor chip.

Advancing miniaturization of optoelectronic components entails more andmore often the requirement for the narrowest possible openings of thecavity and/or for more complex semiconductor chip and wiringarrangements in the cavity. In these cases, for lack of space, the sidewalls of the cavity can often only be formed perpendicularly or at asteep angle with respect to the bottom area of the cavity.

The usually Lambert or even rearwards directed radiation or receptioncharacteristic of the semiconductor chip means, therefore, thatsignificant losses of luminous flux arise and a lower externalefficiency of the component thus arises. Therefore, there is a need foroptoelectronic components which have a sufficiently good efficiencydespite the absence of reflectors, or reflectors that cannot berealized, at the inner areas of their cavities.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an optoelectroniccomponent of the type mentioned in the introduction, which as far aspossible meets the demand outlined above.

This and other objects are attained in accordance with one aspect of theinvention directed to an optoelectronic component including asemiconductor chip having a region for at least one of emitting andreceiving electromagnetic radiation and a reflective filling compoundarranged on a side of the semiconductor chip, wherein a surface of thefilling compound adjacent to the semiconductor chip and facing toward afront side of the optoelectronic component is arranged underneath or atthe most levels with the region of the semiconductor chip for the atleast one of emitting and receiving electromagnetic radiation.

According to another embodiment of the present invention, anoptoelectronic component includes at least one basic housing, which hasa cavity, and at least one semiconductor chip, which is arranged in thecavity and emits and/or receives electromagnetic radiation. The cavityextends from a front side of the basic housing into the basic housing. Areflective filling compound is arranged in the cavity between thesemiconductor chip and side walls of the cavity, of which fillingcompound at least one of its surfaces facing toward the front side ofthe basic housing is curved like a concave mirror, in particularconcavely, as seen from the semiconductor chip, and forms a reflectorarea for part of the radiation.

A method for producing an optoelectronic component includes formation ofthe basic housing with the cavity, positioning of the semiconductor chipin the cavity and filling of a filling compound into the cavity. Thematerial and quantity of the filling compound are chosen in such a waythat relative to a bottom area of the cavity, the filling height (h_(F))thereof adjacent to the semiconductor chip is less than the distancebetween a laterally radiation-emitting and/or-receiving region of thesemiconductor chip and the bottom area, and the surface thereof, as seenfrom the semiconductor chip, curves concavely in its course towards sidewalls of the cavity on account of the adhesion force between thematerial of the filling compound and the material of the side walls, andthe surface is formed as a reflector for the radiation in this way.

The optoelectronic component according to the invention has a basichousing and at least one radiation-emitting and/or -receivingsemiconductor chip in a cavity of the basic housing. Unlike inconventional optoelectronic components, the reflector is at least notsolely realized by reflective side areas of the cavity of the basichousing itself, but rather is realized at least in part by a reflectivefilling compound filled into the cavity. For this purpose, the materialand the quantity of the filling compound are preferably chosen in such away that, during and/or after the filling process, on account of theadhesion force between the material of the filling compound and thematerial of the side areas of the cavity, the filling compound is drawnup at these side areas and forms a surface which is like a concavemirror, in particular is shaped like a parabola. This surface of thefilling compound facing towards the front side of the housing serves asreflector area for electromagnetic radiation emitting and/or received bythe semiconductor chip. The composition of the filling compound isselected, moreover, such that a highest possible proportion of theradiation is subjected to total reflection at the reflector area. Thiscan be achieved by using materials with suitable refractive indices forthe filling compound.

In other words, the cavity is partly filled with the filling compoundand, on account of the adhesion force between filling compound and basichousing, an inner area of the filling compound which is essentially likea concave mirror, in particular concave¹), from the point of view of thesemiconductor chip is automatically established in the cavity since thefilling compound creeps upwards at the lateral inner areas of the cavityof the basic housing. The concave-mirror-like inner areas of the fillingcompound that are thus formed form the reflector for the semiconductorchip inserted into the cavity. ¹note: here and below—in contrast to thepriority application (wherein “convex” is used)—the form of the innerarea is referred to as concave as seen from the chip; as a precaution,it shall already be expressly pointed out at this juncture that the term“concave” used in the present case relates to the same inner areaconfiguration referred to as “convex” in the priority application. Thisis already revealed unambiguously in the priority application simplyfrom the fact that, as expressly described in the priority application,the form of the inner area is formed for example by the filling compoundcreeping upwards at the lateral inner areas of the cavity of the basichousing, and by the filling compound having a parabola-like inner area.

These reflector areas can be produced in a simple manner, even with verysmall openings of the cavities, by means of suitable apportioning of thefilling compound in the cavity. Moreover, the terminals, wirings and thelike which are present in the cavity are enclosed by the fillingcompound without any impairment of their functioning.

Consequently, with the measure according to the invention, even withoptoelectronic components with narrow openings of the cavity and/orcomplex semiconductor chip and wiring arrangements in the cavity, it ispossible to provide reflectors within the cavity and thus to increasethe external efficiency of the components.

In a preferred embodiment of the invention, the material of the fillingcompound contains titanium oxide (TiO₂). In particular, the material ofthe filling compound is preferably an epoxy resin filled with TiO₂particles. Particularly preferably, a proportion of TiO₂ in the fillingcompound (28) is between about 10 and 50% by volume.

In a manner similar to that in the case of conventional optoelectroniccomponents, preferably a free surface of the chip remaining after

mounting of the chip in the cavity and connection of the chip toexternal electrical terminals by means of a bonding wire, for example,and

filling-in of the filling compound

is covered with a radiation-transmissive, in particular transparent,encapsulation compound which encloses the semiconductor chip andpreferably fills the cavity to the greatest possible extent.

The method for producing the optoelectronic component having a basichousing and at least one semiconductor chip in a cavity of the basichousing may, for example, comprise the following method steps:

-   -   (a) formation of a basic housing around a leadframe, the basic        housing having a cavity into which terminals of the leadframe        are introduced;    -   (b) positioning and electrical contact-connection of at least        one radiation-emitting or -receiving semiconductor chip into the        cavity; and    -   (c) partial filling of a filling compound into the cavity, the        material and the quantity of the filing compound being chosen in        such a way that the filling compound, on account of the adhesion        force between the filling compound and the basic housing,        assumes a form which widens essentially conically from bottom to        top in the cavity, and the conical inner areas of the filling        compound serve as reflector.

Preferably, afterwards in a further method step (d), aradiation-transmissive, in particular transparent, encapsulationcompound is filled into the cavity in order to completely enclose thesemiconductor chip in the cavity.

The reflectivity of an epoxy-resin-based filling compound containing aTiO₂ proportion is up to about 80%. In a comparison betweenoptoelectronic components of identical design but with differentlyembodied filling compounds according to the invention or no fillingcompound according to the invention in the cavity, but ratherexclusively with a transparent encapsulation compound for thesemiconductor chip, it was possible to obtain an increase in theexternal efficiency by up to 20% or more based on the filling compoundaccording to the invention.

Further advantages and advantageous developments of the optoelectroniccomponent according to the invention and of the method for producing itemerge from the exemplary embodiments described below in conjunctionwith FIGS. 1 and 2.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a diagrammatic illustration of a sectional view of thefirst exemplary embodiment, and

FIG. 2 shows a diagrammatic illustration of a sectional view of thesecond exemplary embodiment.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

In the two exemplary embodiments, identical or identically actingconstituent parts are provided with the same reference symbols in eachcase.

In the optoelectronic component 10 in accordance with FIG. 1, a basichousing 12 with cavity 18 is formed by encapsulating a leadframe 14 witha suitable plastics material by injection-moulding.

In the cavity 18, there is situated on the leadframe 14 a semiconductorchip 20 which emits and/or receives electromagnetic radiation, forexample a light-emitting diode chip, which emits and/or receives atleast part of the radiation via its side edges. The semiconductor chip20 is connected to an electrical terminal of the leadframe 14 by meansof a bonding wire 22. A reflective filling compound 28 is filled inbetween the semiconductor chip 20 and the side walls 26 of the cavity18, the said filling compound comprising, for example, epoxy resinfilled with TiO₂ particles, the proportion of TiO₂ in the fillingcompound 28 sufficing to significantly increase the reflectivity of thefilling compound 28. The proportion of TiO₂ in the filling compound 28preferably lies between about 10 and 50% by volume. Particles made ofzirconium oxide, zinc oxide, barium sulphate, gallium nitride or amixture of at least two of these types of particles are preferablysuitable for use with an epoxy resin in the filling compound 28. It isimportant that the difference in refractive index between the epoxyresin and the particles is large enough such that the reflectivity ofthe filling compound 28 is increased.

The surface 30 of the filling compound, which faces towards the frontside 121 of the basic housing 12, is curved concavely as seen from thesemiconductor chip 20 and forms a reflector area at least for part ofthe laterally emitted and/or received radiation. Given correspondinggeometry of the component 10 or the radiation characteristic of thesemiconductor chip 20, a reflector area which is convex as seen from thesemiconductor chip is conceivable as an alternative.

In addition to the semiconductor chip 20, a chip carrier substrate 24(not illustrated in the figure) may be arranged between the saidsemiconductor chip and the basic housing 12, the dimensions of whichchip carrier substrate are chosen in such a way that a trench is formedbetween its side edges 241 and the side walls 26 of the cavity 18, thefilling compound 28 being situated in the said trench.

Relative to the bottom area of the cavity 18, the filing height h_(F) ofthe filling compound 28 adjacent to the semiconductor chip 20 is lessthan the distance between the region of the relevant laterally emittingand/or receiving region of the semiconductor chip 20 and the bottomarea. The filling height h_(F) rises beyond the abovementioned distancein its course towards the side wall 26 of the cavity 18.

That free surface region of the semiconductor chip 20 which lies abovethe filling compound is covered by a radiation-transmissiveencapsulation compound 32 and comprises an epoxy resin again, forexample, or another suitable reaction resin.

In the exemplary embodiment in accordance with FIG. 2 externalelectrical terminals 14 are applied on a carrier body 16 comprisingaluminium, for example. The cavity 18 is realized by means of a plastichousing frame 120, which is likewise arranged on the carrier body 16.

In the cavity, two semiconductor chips 20 which emit and/or receiveelectromagnetic radiation, for example two light-emitting diode (LED)chips, are mounted on a chip carrier substrate 24 comprising silicon,for example. The two LED chips are electrically conductively connectedto the electrical terminals 14 via bonding wires 22.

As is clearly discernible in the sectional view of FIG. 2, in the sameway as in the exemplary embodiment described first, the inner areas 26of the cavity 18 are virtually cylindrical, in other words they run verysteeply from the bottom area to the front side of the basic housing 12.These steep side walls 26 have only a negligibly small reflector effect.

Given a uniform bottom area in the cavity, whose minimum size is fixedlypredetermined by the size and number of the chips and/or the spacerequirement for chip mounting and contact-connection, a reduction of thesteepness of the side walls 26 of the cavity would entail an enlargementof the component. This must be avoided in any case on account of thelack of space in many applications. This aim is achieved by means of theinvention.

In the exemplary embodiment in accordance with FIG. 2, the cavity 18 isfilled with a filling compound 28 in the region of the trench betweenthe chip carrier substrate 24 and the side walls 26 of the cavity 18,the said filling compound for example comprising the same material asthe filling compound 28 of the first exemplary embodiment.

As is clearly discernible in the sectional view of FIG. 2, the fillingheight h_(F) of the filling compound 28 adjacent to the semiconductorchips 20, i.e. adjacent to the chip carrier substrate 24, issignificantly smaller than adjacent to the side walls 26 of the cavity18, where the filling compound 28 is drawn up essentially as far as theedge with the front side 121 of the basic housing 12. In this way, thesurface of the filling compound 28 acquires a form opening essentiallylike a parabola towards the front side. Given a suitable choice of thematerial and the apportioning of the filling compound 28, this formresults automatically on account of the adhesion forces between thefilling compound 28 and the material of the housing frame 120. Theconcavely curved inner areas 30 of the filling compound 28 as seen fromthe semiconductor chips 20 serve as reflector for the radiation which isemitted and/or received laterally by the semiconductor chips 20.

The reflectivity of the filling compound 28 containing the TiO₂proportion is up to about 80%. In comparison with an optoelectroniccomponent in which the cavity is exclusively filled with a transparentfilling compound, with the optoelectronic component

of the present invention it was thus possible to increase the externalefficiency by up to 20% or more.

In order to protect the semiconductor chips 20, the cavity 18 iscompletely filled with a radiation-transmissive, for exampletransparent, encapsulation compound 32 which encloses the semiconductorchips 20 and is transmissive for the radiation to be emitted or to bereceived by the semiconductor chips 20. For this encapsulation compound32, it is possible to use, as in the conventional components, suitablefilling compounds comprising transparent synthetic resins, such as epoxyresin, for example, or comprising polycarbonate, which is preferablyespecially coordinated with the properties of the filling compound 28(also applies to exemplary embodiment in accordance with FIG. 1).

It goes without saying that, in both exemplary embodiments, the numberof semiconductor chips 20 in the cavity 18 of the basic housing 12 isnot restricted to one or two; rather, it is also possible for more thantwo semiconductor chips to be mounted in the cavity. In addition, it isalso possible for more than just one cavity 18 to be formed in a basichousing 12.

In order to produce an optoelectronic component 10 in accordance withthe first or second exemplary embodiment, firstly the basic housing 12with the cavity 18 is formed and then the semiconductor chip 20 ismounted in the cavity 18 and electrically conductively connected to theexternal electrical terminals 14. The filling compound 28 issubsequently inserted into the cavity 18. This is done by apportioningsuch that

-   (i) relative to a bottom area of the cavity 18, the filling height    h_(F) of the filling compound adjacent to the semiconductor chip 20    is less than the distance between the laterally radiation-emitting    and/or -receiving region of the semiconductor chip 20 and the said    bottom area, and-   (ii) the surface of the filling compound, as seen from the    semiconductor chip 20, is curved concavely in its course towards the    side walls 26 of the cavity 18 on account of the adhesion force    between the material of the filling compound 28 and the material of    the side walls 26, consequently the filling compound creeps upwards    at the side walls 26.

A surface 30 serving as reflector for the radiation is formed in thisway.

The radiation-transmissive encapsulation compound 32 is subsequentlyfilled into the cavity 18, which covers at least those surfaces of thesemiconductor chip (20) which are still uncovered after the precedingsteps.

It goes without saying that the above description of the invention onthe basis of the exemplary embodiments is not to be understood as arestriction of the invention thereto. Rather, the concept of theinvention set forth in claims 1 and 12 can be employed in a multiplicityof widely different designs.

Thus, while there have shown and described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements and/ormethod steps shown and/or described in connection with any disclosedform or embodiment of the invention may be incorporated in any otherdisclosed or described or suggested form or embodiment as a generalmatter of design choice. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

1. An optoelectronic component comprising: a semiconductor chip having aregion for at least one of emitting and receiving electromagneticradiation; and a reflective filling compound arranged on a side of thesemiconductor chip, wherein a surface of the filling compound adjacentto the semiconductor chip and facing toward a front side of theoptoelectronic component is arranged underneath or at the most levelswith a region of the semiconductor chip for the at least one of emittingand receiving electromagnetic radiation.
 2. The optoelectronic componentaccording to claim 1, wherein the optoelectronic component comprises anelectrical terminal.
 3. The optoelectronic component according to claim2, wherein the filling compound covers at least part of the electricalterminal.
 4. The optoelectronic component according to claim 1, whereinthe optoelectronic component comprises a carrier body.
 5. Theoptoelectronic component according to claim 4, wherein the fillingcompound covers at least part of the carrier body.
 6. The optoelectroniccomponent according to claim 1, wherein the filling compound containsTiO₂.
 7. The optoelectronic component according to claim 6, wherein thefilling compound is an epoxy resin filled with TiO₂ particles.
 8. Theoptoelectronic component according to claim 6, wherein the proportion ofTiO₂ in the filling compound is between about 10 and 50% by volume. 9.The optoelectronic component according to claim 1, further comprising aradiation-transmissive encapsulation compound at least partlyencapsulating the semiconductor chip.
 10. The optoelectronic componentaccording to claim 9, wherein the encapsulation compound covers thesemiconductor chip on a surface facing toward the front side of theoptoelectronic component and extends to the surface of the fillingcompound facing toward the front side of the optoelectronic component.